JPS6351849A - Medical nuclear magnetic resonance diagnostic apparatus - Google Patents

Abstract

(57) [Abstract] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention relates to a medical nuclear magnetic resonance diagnostic apparatus equipped with a refrigerator, and enables reduction of noise caused by vibrations of the refrigerator. The present invention relates to a medical nuclear magnetic resonance diagnostic apparatus.

(Prior Art) To perform medical measurements in a medical nuclear magnetic resonance diagnostic system (commonly known as an MRI apparatus), a uniform and high magnetic field is required. For this reason, superconducting magnets are used in recent MRI apparatuses.

A superconducting magnet is a superconducting electromagnetic coil wound into a coil, and it is necessary to maintain this superconducting electromagnetic coil at a temperature of approximately 4°.

For this reason, conventional MRI apparatuses have structures as shown in FIGS. 4 and 5.

FIG. 4 is an overall sectional view of the MRI apparatus, and (3(1) is the axis into which the sample of the MHI apparatus is inserted.

The superconducting electromagnetic coil (31) is housed in a liquid helium container (33) filled with liquid helium (32) at a temperature of about 4°. The liquid helium container (33) is surrounded by a cylindrical intermediate shield tube (34). The intermediate shield tube (34) is filled with liquid nitrogen (35
), and the liquid nitrogen container (36) is further surrounded by a vacuum container (37). Each intermediate chamber (38) is evacuated and made vacuum tight;
Heat shield. The liquid nitrogen container (36) is a vacuum container (3
7), and the liquid helium container (33) and intermediate shield cylinder (34) are connected to the liquid nitrogen container (36), respectively, with titanium ring hanging rods (301) and (302) having low thermal conductivity.
, (303), and has a structure that is supported flexibly.

As long as the superconducting electromagnetic coil (31) maintains superconductivity, current can flow through the superconducting electromagnetic coil (31) for an infinitely long time.

Therefore, a uniform and high magnetic field required for an MRI apparatus can be obtained. However, liquid helium (32) is required to maintain superconductivity, and liquid helium (32
) is particularly problematic, requiring complex heat shielding in structures such as those described above.

Now, the cost of maintaining this type of superconducting magnet is determined decisively by the amounts of liquid nitrogen (35) and liquid helium (32) used. In this case, this liquid nitrogen (35)
And if the evaporation rate of liquid helium (32) can be kept low, such costs can be kept low.

A refrigerator (41) is attached to a part of the flange (39) of the vacuum container (37) in order to maintain a low evaporation rate of liquid nitrogen or liquid helium.

This refrigerator (41) extends through a vacuum container (37), a liquid nitrogen container (36), and an intermediate shield cylinder (34).
Liquid nitrogen container (36) via the mesh board heat conductor (47)
and actively cools the intermediate shield cylinder (34) via the two-stage mesh plate heat conductor (48).

Next, the configuration of the refrigerator and the mounting stage for the MRI apparatus will be explained using FIG. 5.

The refrigerator (41) has a cooler head (42) and a first-stage cooling section (4
5), consists of a two-stage cooling section (46), and gas piping (304).
Gas helium is supplied from the compressor (4(1)) via the compressor (4(1)).

For example, in the case of a Gifford-McMahon refrigerator (GM refrigerator), the cooling sections (45) and (46) are the first stage cooling section (45).
, a two-stage cooling section (46) both have a depressor inside. This compressor uses piston motion to cycle the compression and expansion of the cold expansion chamber.

On the other hand, the cooler head (42) is composed of a stepping motor that rotates at approximately RPM and a cam mechanism that converts rotational motion into reciprocating motion, for example.

Connected to this reciprocating motion, the dispressor is caused to reciprocate.

Next, the conventional mounting means for the refrigerator (41) is to attach the flange (43) on the refrigerator side to the mounting flange (39) on the vacuum container.
) is completely tightened with a bolt by intervening an O-ring (44).

On the other hand, the internal connection is made using the one-stage mesh plate heat conductor (
47) and a two-stage mesh plate conductor (48), -4 = cools the liquid nitrogen container (36) and the intermediate shield cylinder (34). However, this thermal conductor (47), (4g
) is flexibly connected to the vacuum container (37), liquid nitrogen container (36), and intermediate shield cylinder (34) by using a flat mesh plate made of steel so as to absorb relative displacement.

When a refrigerator is mounted on the vacuum vessel (37) with such a configuration, a problem arises in that the vacuum vessel (37) generates noise at the tolerance level of the MHI device -F. When we investigated the cause, we found the following.

Vibration of the stepping motor, which is part of the refrigerator configuration (
2f, 4f, 6f, . . . f (varnish chipping motor drive frequency) and mechanical vibrations accompanying the reciprocating motion of the dispressor were directly transmitted to the vacuum container (37) forming the outer cylinder. In other words, it has a form similar to the vibration transmission path (49) in FIG. When the vibrations of the refrigerator were transmitted to the vacuum container (37), the vacuum container (37) vibrated and sound was emitted from the surface.

Furthermore, since the vacuum container (37) is made of a metallic material, vibrations are less attenuated, and it has a simple cylindrical shape, making it highly susceptible to vibration. When the vacuum container (37) vibrates and generates sound, it has a direct effect on the body when using an MRI apparatus, posing a major problem in the medical environment.

Medical environment noise is particularly strictly regulated and its noise level is very low. In addition, conventional noise creates fear, and it is especially desirable to reduce the noise level.

(Problems to be Solved by the Invention) As described above, in the conventional MRI apparatus equipped with a refrigerator, the noise caused by the vibration of the refrigerator affects the human body, which is a major problem in the medical environment.

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, it is an object of the present invention to provide a low-noise medical nuclear magnetic resonance diagnostic apparatus (MRI apparatus) by making simple structural changes.

[Structure of the invention]

(Means for Solving the Problems) In order to achieve the second object, the present invention replaces the conventional complete fastening method for connecting the refrigerator (41) and the vacuum container (37) with a weakly elastic one such as a bellows. By creating a structure in which the weight and vacuum pressure load of the refrigerator are fully connected and supported by a part of the inner cylinder such as the liquid nitrogen container (36) or the intermediate shield cylinder (34), the refrigerator (4) can be fully connected and supported. ]) to the vacuum container (37) serving as the outer cylinder is significantly reduced, thereby reducing the radiated sound due to the vibration of the vacuum container (37).

(Function) The present invention connects the refrigerator and the vacuum container with a weakly elastic connection using a bellows, thereby maintaining a vacuum and, moreover, being able to significantly reduce vibration transmission.

The weight and vacuum pressure load of the refrigerator are supported by an inner cylinder such as a liquid nitrogen container or an intermediate shield cylinder. By doing so, the vibrations of the refrigerator are transmitted to the inner cylinder (for example, the liquid nitrogen container or the intermediate shield cylinder), and the inner cylinder vibrates. However, even if the inner cylinder vibrates, its surface is in a vacuum, so the sound from the plate surface is not radiated into the vacuum container. That is, even if sound is emitted from the surface of the inner cylinder, since it is inside the vacuum container, the sound is almost completely insulated, reducing the noise of the MRI apparatus.

(Example) =7- Hereinafter, an example of the present invention will be described with reference to FIGS. 1 and 2. Note that the same reference numerals are used for the same parts described in the conventional structure of FIGS. 4 and 5, and some explanations are omitted.

In Figures 1 and 2, the refrigerator (41) has a flange (43) of the refrigerator and a flange (11) of the bellows (11).
At 12), connect with bolts via the O-ring (44).

Furthermore, the connection with the vacuum container (37) is also made between the flange (39) on the vacuum container side and the flange (13) of the bellows (11).
are connected with bolts via an O-ring (44). The spring constant of this bellows (11) is 1 to 10 kgf/peng,
In this example, the weight was 3 kg/image.

On the other hand, the connection between the first-stage and second-stage cooling sections (45), <46), the liquid nitrogen container (36), and the intermediate shield cylinder (34) has the following structure.

First, the two-stage cooling section (46) and the intermediate shield cylinder (34) are connected by a net plate-shaped heat conductor (48), as in the conventional case, to transfer heat.

Next, the first stage cooling section (45) and the liquid nitrogen container (36) are connected by a flat plate-shaped heat conductor (14), which transfers heat and absorbs the load of the refrigerator (41) over the entire surface. It is a structure that is well received.

The refrigerator portion protruding outside the vacuum container (37) is entirely surrounded by a sound insulating cover (21) made of a non-magnetic metal plate. A sound insulating material (202) with a high specific gravity such as a lead plate is attached to the inner surface of the sound insulating cover (21), and a sound absorbing material (203) such as ceramic fiber is further attached to the inner surface of the sound insulating material (202). Note that the sound insulation material (202) may be formed not only on the inner surface but also on the outer surface of the sound insulation cover (21).

Furthermore, the gas pipe (304) is also surrounded by a sound insulating cover (not shown) as shown in 2.

Next, the operation of the above embodiment will be explained.

Since the dead weight and vacuum pressure load of the refrigerator (41) are rigidly supported by the flat heat conductor (14) that connects the first-stage cooling section (45) and the liquid nitrogen container (36), each cylindrical member part ,
Relative displacements among the vacuum container (37), liquid nitrogen container (36), and intermediate shield tube (34) are absorbed by the bellows (11) and the flexible mesh heat conductor (48). Therefore,
The vibration of the refrigerator (41) is caused by the vacuum container (which is the outer cylinder).
37), the bellows (11) makes it difficult to transmit, and almost all of the liquid nitrogen is transmitted to the liquid nitrogen container (36),
Vibrate the liquid nitrogen container (36). This liquid nitrogen (
36) is located inside the vacuum container (37) and is surrounded by a vacuum, so even if this liquid nitrogen container vibrates, no sound pressure is propagated to the vacuum container (37).

The vibrations of the liquid nitrogen container (36) are transmitted to the vacuum container (37) only by the suspension 301) that connects them. However, this hanging rod (301) is connected flexibly, and only the force in the axial direction of the hanging rod (30i) acts. In addition, since this hanging rod (301) is installed in a location with low vibration sensitivity (a place where vibration is difficult to occur), that is, near the end plate (37a) of the vacuum container, the force that causes the vacuum container (37) to vibrate is weak. be.

In other words, the liquid nitrogen container (36) vibrates in response to the vibrations of the refrigerator (41), and is consumed by converting into its own elastic energy and kinetic energy of the liquid, and the external vacuum container (
37) hardly vibrates.

In addition, the bellows (11) has a spring constant of 3 kgf/m.
However, if the spring constant of the bellows is made softer, the vibration transmission rate decreases in proportion to it, and as a result, the noise of the MRI apparatus can be further reduced.

In order to soften the spring constant of the bellows, it is necessary to increase the number of stages of the bellows or reduce the plate thickness, which results in insufficient fatigue strength against vibration. Therefore, taking both factors into consideration, a bellows with a spring constant of about 1 to 10 kgf/mm is most practical.

Moreover, the refrigerator head (42) is entirely surrounded by a sound insulation cover (21) to which sound insulation material (202) and sound absorption material (203) are attached, and the gas piping (304) is also sound insulation (not shown) similar to the above. Since it is surrounded by a cover, the refrigerator (41),
Noise generated from the gas pipe (304) is also prevented from propagating to the outside.

As a result, noise caused by refrigerator vibration of the MRI apparatus can be significantly reduced.

As another embodiment, the structure may be such that the sound insulating plate and its attached devices are removed, as shown in FIG.

Even in this case, effects similar to those of the embodiments shown in FIGS. 1 and 2 can be obtained.

In addition, as another embodiment, it is also possible to weakly connect the first stage cooling section (45) to the liquid nitrogen container (36) and rigidly connect the second stage cooling section (46) to the intermediate shield cylinder (34). be.

〔Effect of the invention〕

According to the present invention, the refrigerator and the vacuum container are weakly elastically connected with a bellows, and rigidly connected so that the refrigerator's own weight and vacuum pressure load are supported by the liquid nitrogen air temperature or intermediate shield cylinder, which is the inner cylinder. Therefore, the vibration of the refrigerator is isolated by the bellows, and the vibration is not transmitted to the vacuum container, which is the outer cylinder, but most of the vibration is transmitted to the inner cylinder. Only the inner cylinder vibrates, and elastic energy and liquid It is consumed instead of kinetic energy.

As described above, since the refrigerator support structure significantly reduces the vibration of the vacuum container, a low-noise medical nuclear magnetic resonance diagnostic apparatus can be obtained.

[Brief Description of the Drawings] Fig. 1 is a vertical sectional view showing the upper half of an embodiment of the present invention, Fig. 2 is an enlarged view showing the main part of Fig. 1, and Fig. 3 is another embodiment. FIG. 4 is a longitudinal sectional view showing the L half of the conventional example, and FIG. 5 is an enlarged view showing the main part of FIG. 4. DESCRIPTION OF SYMBOLS 11... Bellows, 14... Flat heat conductor, 21... Sound insulation cover, 31... Superconducting electromagnetic coil, 34... Intermediate shield tube, 36... Liquid nitrogen container, 37... Vacuum Container, 41... Freezer, 202... Sound insulation material, 203... Sound absorbing material.

Claims (4)

[Claims] (1) In medical nuclear magnetic resonance diagnostic equipment that generates a magnetic field with a superconducting electromagnetic coil and performs medical measurements using the magnetic field, a refrigerator is installed to maintain the superconducting electromagnetic coil in a superconducting state for a long time. Medical nuclear magnetism characterized in that the means is weakly elastically coupled to an outer cylindrical vacuum container by a bellows, and the load of the refrigerator is rigidly coupled and supported to an inner cylindrical liquid nitrogen container or an intermediate shield cylinder. Resonance diagnostic device. (2) The medical nuclear magnetic resonance diagnostic apparatus according to claim 1, further comprising a sound insulating cover that surrounds a portion of the refrigerator exposed outside the vacuum container. (3) The medical nuclear magnetic resonance diagnostic apparatus according to claim 1 or 2, wherein the bellows has a spring constant of 1 to 10 kgf/mm. (4) Claims characterized in that the sound insulating cover is made of a non-magnetic metal plate, a sound insulating material with a high specific gravity such as lead is attached to the inner surface, and a sound absorbing material such as ceramic fiber is further attached to the inner surface. 2. Medical nuclear magnetic resonance diagnostic apparatus according to item 2.